Why Your getElement() Is Returning null on Java 22

Why Your getElement() Is Returning null on Java 22

The culprit isn’t the JVM “forgetting” your overrides—it’s a subtle signature mismatch between your interface’s generic bounds and the static factory’s bounds. In Java 11 the compiler was more forgiving; Java 22 tightened up method‐override rules so your anonymous implementation no longer overrides the interface defaults, leaving you with the default methods that return null.

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What’s Happening Under the Hood

Your interface declares:

 interface Priority> { default E getElement() { return null; } default P getPriority() { return null; } // … } 

Here P can be any Comparable<?>.

Your static factory is declared as:

 static <V extends Priority<E,P>, E, P extends Comparable<P>> Priority<?,P> createPriorityElement(E element, P prio) { … } 

Now you’ve constrained P extends Comparable<P>—a different bound than the interface’s P extends Comparable<?>.

Because those two P‐bounds don’t match exactly, the compiler generates your anonymous class’s getElement() and getPriority() as new methods, not proper overrides of the interface defaults. At runtime, calling getElement() dispatches to the interface default (returning null) instead of your implementation.

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How to Fix It

1. Unify your P bounds so both interface and factory agree. For example:

    public interface Priority> extends Comparator
    { // … static <E, P extends Comparable<P>> Priority<E,P> create(E element, P prio) { return new Priority<E,P>() { private final E elem = element; private final P pr = prio;
   
   @Override public E getElement() { return elem; } @Override public P getPriority() { return pr; } @Override public int compare(P o1, P o2) { return o1.compareTo(o2); } }; } } 

2. Annotate your overrides with @Override. If the signature doesn’t match, the compiler will flag it immediately.
3. Move main(...) out of the interface into a dedicated class to avoid generic‐main oddities and keep your interface focused on its contract.

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A Cleaner Alternative: A Concrete Holder Class

Instead of an anonymous, generic‐shadowing factory, a simple final class can be more robust:

 public final class PriorityElement> implements Priority {

private final E element; private final P priority;

public PriorityElement(E elem, P prio) { this.element = elem; this.priority = prio; }

@Override public E getElement() { return element; } @Override public P getPriority() { return priority; } @Override public int compare(P o1, P o2) { return o1.compareTo(o2); } } 

Usage:

 var artistPrio = new PriorityElement<>(artist, 10); var pq = new PriorityQueue<Priority<?,Integer>>(new PriorityComparator<>()); pq.offer(artistPrio); System.out.println(pq.peek().getElement()); // now non‐null! 

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Going Further

• If you prefer a one‐liner factory, consider a Java record:

   public record PriorityRec> (E element, P priority) implements Priority { @Override public int compare(P o1, P o2) { return o1.compareTo(o2); } } 

• Always recompile your entire codebase when upgrading major JDKs—stale .class files can hide these binding issues.
• Use javap –c on your interface and anonymous class to inspect which methods actually get generated and overridden.